The Effect of Surface Condition on Wetting of HASTELLOY® X by Brazing Filler Metal of Ni-Pd-Cr-B-Si System

The paper presents the results of wettability tests by a sessile drop method coupled with residual gas analysis for the HASTELLOY® X substrates contact heated with brazing filler metal of Palnicro 36M. The contact angles formed between the substrate and the molten brazing filler metal were recorded by high-speed high-resolution CCD camera using two different heating procedures: (1) fast continuous heating to a temperature of 960 °C; (2) isothermal heating at a temperature of 995 °C for 10 min after step heating to the test temperature. In this study, the reference sample was HASTELLOY® X in a delivery state (D1). The base material with a different surface finish was also tested: after polishing (P1), after polishing and oxidation at a temperature of 600 °C for 1 h in the air (U1). The tests confirmed very good wetting properties of Palnicro 36M on HASTELLOY® X, independently on its surface finish and the heating procedure used in this study, i.e., after 10 min at 995 °C, the final contact angle values were θf = 7.6 ± 0.1°, 6.03 ± 0.07° and 6.2 ± 1.0° for D1, P1 and U1, respectively. However, oxidation of HASTELLOY® X surface affects the wetting kinetics and spreading of molten Palnicro 36M on BM substrates by: (1) increasing the initial contact angle values (θ0 = 51 ± 4°, 65 ± 13° and 83 ± 2° for D1, P1 and U1, respectively), (2) delaying the wetting process and (3) reducing the spreading area since after wettability tests at 960 °C, the largest area covered with solidified Palnicro 36M drop was noted for D1 (92 mm2) while the smallest one for U1 (52 mm2).